1. Field of the Invention
The present invention relates to a continuously variable hydraulic transmission for use on a motor vehicle and a control lever assembly for controlling such a continuously variable hydraulic transmission.
2. Description of the Relevant Art
Some motor vehicles such as power-propelled lawn mowers, cultivators, or snowplows incorporate a hydraulic transmission which includes an oil pump and an oil motor. The rotative power of the output of the engine on the motor vehicle is transmitted to drive wheels after it is changed in speed by the hydraulic transmission. Such hydraulic transmissions are disclosed in Japanese Laid-Open Patent Publication No. 63(1988)-301133 and Japanese Laid-Open Utility Model Publication No. 63(1988)-191121, for example.
The hydraulic transmission disclosed in the former publication has a directional control valve disposed in an oil passage. The directional control valve brings into fluid communication an oil passage which interconnects the outlet port of an oil pump and the inlet port of an oil motor and an oil passage which interconnects the inlet port of the oil pump and the outlet port of the oil motor, so that the oil motor is freely rotatable. Regardless of whether the oil pump produces an oil pressure or not, the drive wheels coupled to the oil motor are freely rotatable, allowing the operator of the motor vehicle to manually move the motor vehicle freely forwardly or rearwardly.
The directional control valve is connected to a clutch lever by a wire which is different from a wire interconnecting a transmission swash plate and a transmission shift lever. Since the joint between the directional control valve and the connecting wire is exposed out of a casing, a dust cover or the like must be used to prevent foreign matter such as grass clippings or dust from entering the casing. If the clutch lever were gripped while the transmission shift lever is shifted in a high-speed position when the motor vehicle is started, the motor vehicle could not be started smoothly. Therefore, the operator is required to operate the clutch lever after the transmission shift lever is shifted into a low-speed position.
The latter publication shows a power-propelled lawn mower in which various control levers are attached to a handle which extends rearwardly and upwardly from the vehicle body. Normally, the operator operates a transmission shift lever and a clutch lever which can make drive wheels freely rotatable.
The transmission shift lever and the clutch lever are independently connected to the hydraulic transmission by wires which extend under tension along the handle. Since there are plural wires employed, however, the mechanism associated with the wires is complex. There has been an attempt to employ a single wire which would control the transmission shift wire and the clutch wire. However, it would be difficult to employ a single wire because the clutch lever swings through a constant stroke whereas the transmission shift lever is tilted through an angle that varies depending on a desired transmission or speed-reduction ratio.